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ttokoro
21-Topaz I
21-Topaz I
September 26, 2022
Solved

Find the minimum length, l, of role paper required.

  • September 26, 2022
  • 1 reply
  • 3184 views

Making one cone with cap out of a role paper of 12 cm in width. Cone has θ in center angle. Cap and cone have largest areas and each with one piece.
Find the minimum length, l(θ), of role paper required.
If θ=90deg, then l=15 cm is the answer.

image.png

 

Best answer by Werner_E

I understand what you do. I just think its inconsistent to forbid making the cone larger than 12 cm side length (like in Lucs 45° solution) but accept to make it smaller for angles larger than 180°. Just my 2 cent.

I would rather stay with "largest surface but minimal paper" throughout or with constant side length 12 cm and minimal paper (which would allow only angles from 0 to pi.

Here a numerically derived solution for the latter:

Cone.gif

1 reply

23-Emerald IV
September 29, 2022

You can add to the table:

LucMeekes_3-1664447672952.png

Success!
Luc

ttokoro
21-Topaz I
ttokoro21-Topaz IAuthor
21-Topaz I
September 29, 2022

Thanks, challenge this puzzle.  θ=90 degree is the Entrance Exam of High school in Japan. It requires the position of cap and the length of role paper with minimum length.  My answer of the one of 45 degree is here. l=12/sqrt(2).

image.pngimage.pngimage.png

image.pngimage.pngimage.png

t.t.
23-Emerald IV
September 29, 2022

Hmm,

Note that the cone height is not specified.

When cone and cap  have 'largest areas' (possible, given the width of the paper roll)

I get this for theta=45 deg:

LucMeekes_0-1664464369994.png

And here the paper length required is 12 *sqrt(2).

The smaller theta, the longer the paper required...

But also, the higher the cone.

 

Success

Luc